Anti-viral drugs
Viruses have no cell wall and made up of nucleic acid components
Viruses containing envelope – antigenic in nature
Viruses are obligate intracellular parasite
They do not have a metabolic machinery of their own – uses host enzymes
Anti-viral drugs
Certain viruses multiply in the cytoplasm but others do in the nucleus
Most multiplication take place before diagnosis is made
Anti-Viral drugs
Many antiviral drugs are Purine or Pyrimidine analogs.
Many antiviral drugs are Prodrugs. They must be phosphorylated by viral or cellular enzymes in order to become active.
Anti-viral agents inhibits active replication so the viral growth resumes after drug removal.
Anti-viral drugs
Current anti-viral agents do not eliminate non-replicating or latent virus
Effective host immune response remains essential for the recovery from the viral infection
Clinical efficacy depends on achieving inhibitory conc. at the site of infection within the infected cells
Anti-viral drugs
Stages of viral replication
Cell entry – attachment
- penetration
Uncoating
Transcription of viral genome
Translation
Assembly of virion components
Release
Anti-viral drugs
Anti-herpes virus agents
Acyclovir / Valacyclovir
Famciclovir / Penciclovir
Ganciclovir / Cidofovir
Foscarnet
Trifluridine / Idoxuridine / Vidarabine
Anti-viral drugs
Acyclovir & Congeners : Valacyclovir is a prodrug of Acyclovir with better
bioavailability.
Famciclovir is hydrolyzed to Penciclovir and has greatest bioavailability.
Penciclovir is used only topically whereas Famciclovir can be administered orally.
Anti-Viral drugs
PHARMACOLOGY OF ACYCLOVIR AND CONGENERS
Acyclovir, Valacyclovir, Ganciclovir, Famciclovir, Penciclovir all are guanine nucleoside analogs.
Anti-viral drugs
Mechanism of action of Acyclovir and congeners :
All drugs are phosphorylated by a viral thymidine-kinase, then metabolized by host cell kinases to nucleotide analogs.
The analog inhibits viral DNA-polymerase
Only actively replicating viruses are inhibited
Anti-viral drugs
Acyclovir is thus selectively activated in cells infected with herpes virus.
Uninfected cells do not phosphorylate acyclovir.
Anti-Viral drugs
Antiviral spectrum :
Acyclovir: HSV-1, HSV-2, VZV, Shingles.
Ganciclovir / Cidofovir : CMV
Famciclovir : Herpes genitalis and shingles
Foscarnet : HSV, VZV, CMV, HIV
Penciclovir : Herpes labialis
Trifluridine : Herpetic keratoconjunctivitis
Anti-Viral drugs
Pharmacokinetics of Acyclovir :
Oral bioavailability ~ 20-30%
Distribution in all body tissues including CNS
Renal excretion: > 80%
Half lives: 2-5 hours
Administration: Topical, Oral , IV
Anti-viral drugs
Adverse effects of Acyclovir / Ganciclovir
Nausea, vomiting and diarrhea
Nephrotoxicity - crystalluria, haematuria, renal insufficiency
Myelosuppression – Neutropenia and thrombocytopenia – Ganciclovir
Anti-viral drugs
Therapeutic uses :
Acyclovir is the drug of choice for:
HSV Genital infections
HSV encephalitis
HSV infections in immunocompromised patient
Ganciclovir is the drug of choice for:
CMV retinitis in immunocompromised patient
Prevention of CMV disease in transplant patients
Anti-viral drugs
Cidofovir :
It is approved for the treatment of CMV retinitis in immunocompromised patients
It is a nucleotide analog of cytosine – no phosphorylation required.
It inhibits viral DNA synthesis
Available for IV, Intravitreal inj, topical
Nephrotoxicity is a major disadvantage.
Anti-viral drugs
PHARMACOLOGY OF VIDARABINE
Vidarabine is a nucleoside analog. (adenosine)
Antiviral spectrum of Vidarabine :
HSV-1, HSV-2 and VZV.
Its use is limited to HSV keratitis only
Anti-viral drugs
Vidarabine
The drug is converted to its triphosphate analog which inhibits viral DNA-polymerase.
Oral bioavailability ~ 2%
Administration: Ophthalmic ointment
Used in HSV keratoconjunctivitis in immunocompromised patient.
Anemia and SIADH are adverse effects.
Anti-viral drugs
PHARMACOLOGY OF TRIFLURIDINE
Trifluridine is a Pyrimidine nucleoside analogs -inhibits viral DNA synthesis.
Antiviral spectrum Trifluridine :
HSV-1, HSV-2 and VZV.
Use is limited to Topical - Ocular HSV Keratitis
Anti-viral drugs
PHARMACOLOGY OF FOSCARNET
Foscarnet is an inorganic pyrophosphate analog
It directly inhibits viral DNA and RNA -polymerase and viral inverse transcriptase (it does not require phosphorylation for antiviral activity)
Anti-viral drugs
Foscarnet
HSV-1, HSV-2, VZV, CMV and HIV.
Oral bioavailability ~ 10-20%
Distribution to all tissues including CNS
Administration: IV
Anti-viral drugs
Adverse effects of Foscarnet
Hypocalcemia and hypomagnesemia (due to chelation of the drug with divalent cations) are common.
Neurotoxicity (headache, hallucinations, seizures)
Nephrotoxicity (acute tubular nephrosis, interstitial nephritis)
Anti-viral drugs
Therapeutic uses of Foscarnet
It is an alternative drug for
HSV infections (acyclovir resistant / immunocompromised patient )
CMV retinitis (ganciclovir resistant / immunocompromised patient )
Anti-viral drugs
Respiratory viral infections
Influenza –
Amantadine / Rimantadine
Oseltamivir / Zanamavir(Neuraminidase inhibitors)
RSV bronchiolitis –
Ribavirin
Anti-viral drugs
Amantadine and Rimantadine : Influenza
Prevention & Treatment of influenza A
Inhibition of viral uncoating by inhibiting the viral membrane protein M2
Influenza A virus
Amantadine has anti-parkinsonian effects.
Anti-viral drugs
Pharmacokinetics of Amantadine
Oral bioavailability ~ 50-90%
Amantadine cross extensively BBB whereas Rimantadine does not cross extensively .
Administration: Oral
Anti-viral drugs
Neuraminidase inhibitors : Influenza Oseltamivir / Zanamavir
Influenza contains an enzyme neuraminidase which is essential for the replication of the virus.
Neuraminidase inhibitors prevent the release of new virions and their spread from cell to cell.
Anti-viral drugs
Neuraminidase inhibitors : Influenza Oseltamivir / Zanamavir
These are effective against both types of influenza A and B.
Do not interfere with immune response to influenza A vaccine.
Can be used for both prophylaxis and acute treatment.
Anti-viral drugs
Anti-viral drugsNeuraminidase inhibitors : Influenza
Oseltamivir / Zanamavir
Oseltamivir is orally administered.
Zanamavir is given intranasal.
Risk of bronchospasm with zanamavir
Anti-viral drugs
PHARMACOLOGY OF RIBAVIRIN
Ribavirin is a guanosine analog.
Inhibition of RNA polymerase
Antiviral spectrum : DNA and RNA viruses are susceptible, including influenza, parainfluenzaviruses, RSV, Lassa virus
Anti-viral drugs
Ribavirin : RSV
Distribution in all body tissues, except CNS
Administration : Oral, IV, Inhalational in RSV.
Anemia and jaundice are adverse effects
Not advised in pregnancy.
Anti-viral drugs
Therapeutic uses Ribavirin
Ribavirin is the drug of choice for:
RSV bronchiolitis and pneumonia in hospitalized children (given by aerosol)
Lassa fever
Ribavirin is an alternative drug for:
Influenza, parainfluenza, measles virus infection in immunocompromised patients
Anti-viral drugs
Hepatic Viral infections :
Interferons
Lamivudine – cytosine analog – HBV
Entecavir – guanosine analog – HBV – lamivudineresistance strains
Ribavirin – Hepatitis C (with interferons)
Anti-viral drugs
Interferons
Interferons (IFNs) are natural proteins produced by the cells of the immune systems in response to challenges by foreign agents such as viruses, bacteria, parasites and tumor cells.
Antiviral, immune modulating and anti-proliferative actions
Three classes of interferons – α , β, γ
Anti-viral drugs
Interferons
α and β interferons are produced by all the cells in response to viral infections
γ interferons are produced only by T lymphocyte and NK cells in response to cytokines – immune regulating effects
γ has less anti-viral activity compared to α and β interferons
Anti-viral drugs
Mechanism of action of Interferons :
Induction of the following enzymes:
1) a protein kinase which inhibits protein synthesis
2) an oligo-adenylate synthase which leads to degradation of viral mRNA
3) a phosphodiesterase which inhibit t-RNA
The action of these enzymes leads to aninhibition of translation
Anti-viral drugs
Antiviral spectrum : Interferon α Includes HBV, HCV and HPV.
Anti-proliferative actions may inhibit the growth of certain cancers - like Kaposi sarcoma and hairy cell leukemia.
Anti-viral drugs
Pharmacokinetics : Interferons
Oral bioavailability: < 1%
Administered Intralesionally, S.C, and I.V
Distribution in all body tissues, except CNS and eye.
Half lives: 1-4 hours
Anti-viral drugs
Adverse effects of Interferons
Acute flu-like syndrome (fever, headache)
Bone marrow suppression (granulocytopenia, thrombocytopenia)
Neurotoxicity (confusion, seizures)
Cardiotoxicity - arrhythmia
Impairment of fertility
Anti-viral drugs
Therapeutic uses Interferons
Chronic hepatitis B and C (complete disappearance is seen in 30%).
HZV infection in cancer patients (to prevent the dissemination of the infection)
CMV infections in renal transplant patients
Condylomata acuminata (given by intralesional injection). Complete clearance is seen ~ 50%.
Hairy cell leukemia (in combination with zidovudine)
AIDS related Kaposi’s sarcoma
Virus DiseasesDrug(s) of choice
Alternative drugs
FLU A
Influenza Amantadine Rimantadine
RSVPneumonia,bronchiolitis
Ribavirin(aerosol)
HSV Genital herpes Acyclovir Foscarnet
KeratitisConjunctivitis
TrifluridineIdoxuridineVidarabine
Encephalitis Acyclovir
Neonatal HSV infection
Acyclovir Vidarabine
Herpes infections in immuno-compromised host
Acyclovir Foscarnet
VZVIn normal host No therapy
In immunocompro-mised host, or during pregnancy
Acyclovir Foscarnet
CMV Retinitis Ganciclovir Foscarnet
HIV AIDSHIV antibody positive with CD4 count < 500/mm3
Zidovudine ±
protease inhibitors
Didanosine,Stavudine
HBVHCV
Hepatitis B, C Interferons
